Typically, iron ore is converted to steel through basic processes that have been known for many years. These processes usually involve the conversion of iron ore to pig iron in a blast furnace using coke produced in a coke oven, and the subsequent conversion of the pig iron, or hot metal, to steel in an open hearth or basic oxygen furnace. However, the high energy and capital costs involved with making steel in the traditional manner have created a demand for new, less expensive methods for producing steel. More specifically, a great deal of effort has been directed to the elimination of the blast furnace and the coke oven in steel-making. Blast furnaces use large quantities of energy, the cost and availability of which is becoming more and more uncertain. Additionally, coke ovens are a large source of pollutants, and modifications to existing coke ovens to meet government regulations are becoming prohibitively expensive.
Accordingly, some effort has been directed to the conversion of iron ore directly to iron carbide followed by the production of steel from the iron carbide, thereby eliminating the blast furnace step.
In this regard, U.S. Pat. No. Re. 32,247 by Stephens, Jr. discloses a process for the direct production of steel. Iron oxides in iron ore are converted to iron carbide, and steel is then produced directly from the iron carbide in a basic oxygen furnace or electric furnace. The electric furnace is typically an electric arc furnace, although it is possible to use other electric furnaces, such as an induction furnace. In the direct production process, the iron oxides in the iron ore are reduced and carburized in a single operation using a mixture of hydrogen (as a reducing agent) and carbon bearing substances (as carburizing agents). The process is typically carried out in a fluidized bed reactor. Steel is then produced by introducing the iron carbide into a basic oxygen furnace or electric furnace, with the blast furnace step being eliminated.
While the process of Stephens, Jr. has proven to be an important advance in the art, a need exists for further improvements in this method of directly producing steel. For example, in the step of converting the iron oxides into iron carbide, even minor variations in the process parameters can cause inferior results, e.g. minor variations in the interrelated process parameters of temperature, pressure and gas composition can cause free iron (Fe) or a variety of iron oxides such as Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, and FeO to be produced rather than iron carbide.
A problem associated with the process is the use of a standard fluidized bed reactor. In such a reactor, rapid mixing of fresh feed with the material in the bed takes place. This mixing results in unreacted ore being transported to the discharge point, thus producing a product containing reacted and unreacted constituents. Another problem with standard reactor bed assemblies is that there may be an uneven pressure drop from the windbox to the reactor bed, leading to an uneven distribution of gases. Orifice plates used to regulate the drop in pressure are often limited in use, since there may be no means to control the total pressure drop. Further, orifice plates tend to expand when heated, and result in cracking of the plate or the surrounding walls. Large orifice plates also tend to sag when subjected to high heat.
The present invention provides a novel reactor design that overcomes the various problems in the prior art and enables the production of a high quality end-product.